What To Know
- It occurs when a massive object, such as a galaxy or galaxy cluster, creates a curvature in spacetime sufficient to bend the path of light from a light source behind the massive object.
- The type and extent of the distortion depends primarily on the mass of the lensing object and the alignment between the light source, the lensing object, and the observer on Earth.
- This massive galaxy bends the light from the quasar in such a way that it creates a spectacular arc of light as well as four separate images of the quasar.
What is a gravitational lens?
A gravitational lens is an astrophysical phenomenon predicted by the general theory of relativity.Albert Einstein. It occurs when a massive object, such as a galaxy or galaxy cluster, creates a curvature in spacetime sufficient to bend the path of light from a light source behind the massive object. This effect is similar to that of an optical lens that bends and focuses light. The mass of the deflecting object can then distort or amplify the light from the distant source. Gravitational lenses can also manifest in a variety of forms, ranging from faint arcs to complete rings, often called Einstein rings, or multiple images of the same light source. The type and extent of the distortion depends primarily on the mass of the lensing object and the alignment between the light source, the lensing object, and the observer on Earth. This phenomenon allows astronomers to discover objects that would otherwise be too distant or faint to detect directly. By analyzing how light is bent, scientists can also infer the presence and amount of dark matter, as well as the properties of dark energy, which play a key role in accelerating the expansion of the universe. Gravitational lenses are therefore a powerful tool for exploring and understanding the deep universe. Several months ago, astronomers used the James Webb Space Telescope to observe one of these phenomena.
A fascinating example of a lensed quasar
In detail, quasars are extremely bright sources powered by supermassive black holes at the centers of distant galaxies. Their intense luminosity allows them to be observed over great distances. When a quasar is aligned with a massive galaxy located between it and Earth, the gravity of this galaxy bends the light from the quasar, creating multiple images of the same quasar. These images can appear as arcs or points of light arranged around the lensing galaxy. Lensed quasars are of great interest to astronomers because they allow them to study several aspects of the universe. By observing multiple images of a lensed quasar, scientists can notably measure the mass distribution of the galaxy or galaxy cluster that acts as a lens, including dark matter that cannot be seen directly. In addition, the variations in brightness between different images of the quasar can provide information on the expansion rate of the universe and the structure of space-time. Finally, lensed quasars offer an indirect method to observe and analyze the properties of the quasars themselves, as well as the host galaxies that house them. The quasar here is named RX J1131-1231. The image was taken with the telescope’s Mid-Infrared Instrument (MIRI) as part of an observational program to study dark matter. 
What do these observations teach us?
The quasar RX J1131-1231 is a fascinating cosmic source and particularly useful for astronomers due to its unique characteristics. This quasar is located about six billion light-years from Earth and is considered one of the best examples of a gravitationally lensed quasar ever discovered. The gravitational lens is formed by a massive galaxy located between Earth and the quasar, about 3.8 billion light-years away. This massive galaxy bends the light from the quasar in such a way that it creates a spectacular arc of light as well as four separate images of the quasar. The observations revealed astonishing details about the supermassive black hole located at its center. In particular, astronomers were able to determine that it is rotating at more than half the speed of light. This conclusion comes from the analysis of the spectrum of light emitted by the accretion disk surrounding the black hole, made up of material attracted by the object as it heats up and spirals inward. When matter is extremely close to the black hole, the speed of rotation of the black hole influences the spectrum of the light emitted. Theoretical models can then link the characteristics of this spectrum to the speed of rotation of the black hole. These data can also provide clues about its formation and evolution history. The rapid rotation of this black hole suggests that it probably grew through mergers with other black holes or galaxies, rather than through the steady accretion of matter from all directions. More precisely, when two black holes merge, they combine their angular momentum, which can lead to rapid rotation. Source: ESA
